| Due to the advantages of abundant reserves,low price,and low standard electrode potential of potassium,potassium ion battery(PIB)has been regarded as one of ideal low cost secondary battery systems and has received extensive attention and research.However,due to the large K+ radius,the volume of electrode material changes seriously during the potassiation/depotassiation process,which has effects on its cycling performance and rate performance.In order to develop low-cost and high-performance carbon-based anode materials for potassium ion batteries,the following works were carried out in this thesis:Hard carbon with disordered structure was prepared by carbonizing biowaste rice husks at high temperature.The effects of carbonization temperature on morphology,structure and potassium storage properties of hard carbon were studied.The results show that the rice husk-based hard carbon anode material has a large interlayer spacing and a unique "micropore-mesoporous" structure,which can reduce the volume expansion during the potassiation process.As the carbonization temperature increases,the pore size of the hard carbon material shrinks and the specific surface area decrease.Electrochemical experimental results show that the rice husk-based hard carbon anode material has excellent cycling performance and rate performance.It has a reversible specific capacity of 244.99 mAh·g-1 at 30 mA·g-1.The reversible specific capacity still maintains 204.25 mAh·g-1 after 100 cycles,and the capacity retention rate is 83.37%.When the current density is increased to 500 mA·g-1,the reversible specific capacity is 103.77 mAh·g-1 after 500 cycles.By using low-cost CaCO3 as template and sucrose as carbon source,a kind of porous carbon anode materials for PIB was prepared by the template method.The material has disordered microstructure,large specific surface area and hierarchical porous structure which is composed by macropore,mesopore and micropore.Electrochemical test results show that this kind of porous carbon anode material has reversible specific capacity of 259.5 mAh·g-1 at 50 mA·g-1.The capacity retention rate is 92.8%after 100 cycles.The surface of cycled electrode is smooth and no obvious cracks appear,indicating that the volume of the material chages little during the potassiation/depotassiation process.At a high current density of 2000 mA·g-1,the specific capacity is 129.6 mAh·g-1 after 10,000 cycles,indicating that the material has good rate properties.FeP/C composite was prepared by a low-cost and high-efficiency high-energy ball milling method with iron powder,red phosphorus and carbon black as raw materials.The results show that nano FeP particles are covered with a layer of amorphous carbon.The carbon layer improves the conductivity of the material,suppresses the volume change of FeP during the charge and discharge process and enhance stability.FeP/C composite has a reversible specific capacity of 218.26 mAh·g-1 and the capacity retention rate is 81.81%after 100 cycles.Potassium storage capacity and cycling stability of FeP/C composite is much better than those of FeP.The functional theory calculation results show that the K+diffusion barrier in FeP is smaller than the Na+ diffusion barrier in FeP and the K+diffusion rate is larger.The electrochemical rate performance of FeP/C composite in PIB is better than that in SIB,which was proved by experiment.The electrochemical performances and interfacial properties of commercial hard carbon anode material in lithium ion battery,sodium ion battery and potassium ion battery were compared.The composition and stability of the SEI film on the surface of the commercial hard carbon were studied by XPS and TOF-SIMS.The results show that commercial hard carbon anode materials exhibit good cycle performance at 30 mA·g-1 in lithium ion battery,sodium ion battery and potassium ion battery.THE SEI film formed on the surface of hard carbon anode material is composed of inorganics and organics.However,due to the high solubility of organic potassium compounds in the electrolyte,the organic compounds on the surface of SEI film dissolved in the electrolyte,which leads the poor stability of the SEI film. |
